This application claims priority from Japanese Application No. 11-208875, filed Jul. 23, 1999, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a liquid dispenser for liquid reagents, liquid samples and the like and, more specifically, to a holder-exchanger of such a dispenser for holding or replacing its dispensing tips.
2. Prior Art
In hospitals and various other institutions where blood test, immunological examination, chemical reaction, and other tests are carried out, it is customary that the blood, sample, reagent, or other object to be tested (hereinafter collectively called xe2x80x9cliquidxe2x80x9d) is simultaneously distributed in predetermined amounts among a number of wells, cuvettes, or other small containers (hereinafter simply called xe2x80x9cwellsxe2x80x9d) using as many dispensing tips.
FIGS. 1 to 3 illustrate a liquid dispenser embodying the present invention. Except the mechanism for holding and replacing dispensing tips, the construction of the apparatus is known to the art. With this in view, a liquid dispenser of the prior art will now be explained with reference to the drawings.
FIG. 1 is a front view of the liquid dispenser, FIG. 2 is a side view, and FIG. 3 is a plan view of a stage assembly of the dispenser. The apparatus includes a horizontal base 1 and a housing frame of upright support 2. The horizontal base 1 carries an X stage 3 movably in the X direction, and the X stage 3 supports thereon a Y stage 5 movably in the Y direction. The Y stage 5 in turn carries, by means of a frame plate 7, a tip rack 9 having an array of holes (in 8 rows and 12 columns) arranged in order to hold a number of tips, at least one plate 11 having holes to support a number of wells in an equidistantly spaced arrangement of the same number, and a reagent or wash tank 13 holding a reagent or wash as the case may be. The X and Y stages 3, 5 can be driven independently of each other by an X-axis drive motor 15 or Y-axis drive motor 17 at a command from a control console.
The upright support 2 supports a Z-axis-movable dispensing head 19, which carries plungers 21 and cylinders 23 in the same numbers and at the same intervals as the holes of the tip rack 9 and plate 11. Tips 100 or 102 (usually either type, although two types are shown here) are fitted to nozzles that constitute the lower ends of the cylinders 23. The dispensing head 19 is driven as a whole in the Z-axis direction by a Z-axis drive motor 27, and the plungers 21 are driven by an S-axis motor 79.
In operation, the X and Y stages 3, 5 are first driven to align the tip rack 9 to the nozzles of cylinders 23, the dispensing head 19 is lowered in the Z-axis direction until the nozzle tips are fitted airtightly in the bores at the upper ends of dispensing tips 100 or 102 so that all the tips 100 or 102 are held by the nozzles, and then the dispensing head 19 is moved up. Next, the reagent tank 13 is aligned just below the nozzles holding the tips 100 or 102, the dispensing head 19 is lowered, bringing the lower ends of the dispensing tips 100 or 102 into the reagent tank 13, the plungers 21 are moved upward to draw by suction predetermined amounts of the reagent, and thus the dispensing head 19 is raised. Then the plate 11 is brought in place under the nozzles holding the dispensing tips 100 or 102, the dispensing head 19 is lowered to position the tips 100 or 102 immediately above the wells containing the sample (blood or the like). Finally, the plungers 21 are forced downward to dispense the reagent into the sample wells.
The nozzles of the prior art constitute the lower ends of the cylinders, and the combinations of many cylinders and plungers arranged in an orderly manner are supported by a single supporting block. The amount to be dispensed depends on the size of the tips, and the outside diameter of the nozzles to fit in the holes at the ends of the tips must be changed in accordance with the dispensing amount. To meet this requirement, it has been common with conventional dispensers to provide a variety of support blocks that hold the plunger-cylinder combinations having nozzles designed for particular amounts to be dispensed and replace the whole unit of support block when required.
The necessity of providing a plurality of dispensing blocks, each of which having a number of plunger-cylinder combinations with nozzles carried by a support block, for different sizes of nozzles has made the dispensers expensive because their dispensing blocks call for high precision in manufacture. Moreover, the replacement of dispensing blocks is cumbersome and not easy.
The present invention solves the problems of the prior art by providing a dispenser in which nozzles are separated from cylinders and are supported by a common block as a nozzle block which alone can be replaced with another one when the necessity arises.
Thus the invention provides a liquid dispenser characterized by a dispensing head which is movable upward and downward as a whole and comprises a plurality of plungers supported by a plunger plate, drive means for moving the plunger plate upward and downward, a plurality of cylinders in which the plungers slidably fit, and a plurality of nozzles arranged at the lower ends of the cylinders and having configurations adapted to engage airtightly with holes for holding specific dispensing tips, the plurality of nozzles being supported by a single nozzle holder, which is built to be detachable from said dispensing head.
According to the invention, only the nozzle holder that support nozzles has to be replaced with another holder conforming to dispensing tips of different dimensions. The arrangement facilitates the replacement and make the dispenser available at lower cost.
The nozzles preferably have an annular extended head each and are loosely fitted in the support block, simply as inserted from above into the block. They are fitted in the holes at the upper ends of the dispensing tips by self-aligning and thereby achieve positive airtight engagement with the tips.
In a preferred form of the invention, an elastic seal plate such as of silicone rubber having openings aligned to the bores of the nozzles and cylinders is sandwiched between the upper surface of the nozzle holder and the plunger-cylinder block, whereby airtight fluid communication is easily established between the nozzles and cylinders.
In another preferred form of the invention, the means for attaching and detaching the nozzle holder in a predetermined point comprises vertical clamp plates having clamps adapted to be engaged with lower edges of the nozzle holder, elastic members that normally bias the clamp plates upward, and means for pressing the clamp plates downward against the urgings of the elastic members. The means for pressing the clamp plates downward may be a plunger plate and means for driving it. Once the clamp plates are forced downward, the nozzle holder descends too under its own weight to the point where it can be pulled off horizontally to replace with a nozzle holder carrying nozzles of a different size.
In a further preferred form of the invention, an eject plate is located under the nozzle holder to remove all dispensing tips simultaneously from the nozzles. The eject plate has a plurality of holes to allow the nozzles to extend through them with tip-fitting ends of the nozzles protruding beyond the bottom of the eject plate. The diameter of the holes of the eject plate is smaller than the outside diameter of the upper ends of the dispensing tips. The eject plate, when forced downward by the bottom surfaces of the clamps of clamp plates, can simultaneously release and remove all tips simultaneously from the nozzles. The plate is normally biased toward the nozzle plates by springs provided on the nozzle holder. As an alternative, the eject plate may be pressed downward by means other than the clamp plates.